The present invention relates to a method of producing sectional strips and sectional sheets having different thicknesses over their widths and to sectional strips and sectional sheets produced by the method.
Sections produced by extrusion, particularly closed hollow sections, can be extruded with different wall thicknesses. But a minimum wall thickness of at least 1.2 mm is required in the thinnest regions. Sections with thinner wall thicknesses may be produced only from thinner sheets by folding or roll forming. But, they then have the same wall thickness throughout, which corresponds to the greatest required wall thickness.
For lightweight structural sections, the greatest wall thickness is often required only in specific regions, for strength, while lesser wall thicknesses are acceptable for use in other regions. Such lightweight structural sections are particularly desired in automotive engineering, to save as much weight as possible on the vehicle.
Cold rolling strips or sheets, in particular of aluminum or aluminum alloys, cannot produce different thicknesses, since the thinner regions suffer a considerably greater degree of deformation than the thicker regions and are therefore stretched considerably more in length than the thicker regions. This causes backward slip of material ahead of the roll groove in the thinner region, with consequent wave formation and finally leads to tearing of the strip or sheet passed through the rolling stand.